I think obviously Stell wanting to go to the church tent meeting and choosing to carelessly take a shortcut in an unfamiliar place led to Mary's death as they could see from the time they pulled into the motel that the townspeople's attitude towards Blacks was particularly hostile and that there was a curfew in effect. The fact that they put Mary in that situation is disturbing to me and I wonder why she agreed to walk back in this unfamiliar place. Stell and Jubie just stood there and didn't take up for her either as she was dragged away by people who voiced that they would do something bad to her and I don't know why.